An air-hydraulic tool for setting a blind rivet is known comprising a housing forming an air chamber, a liquid-filled hydraulic chamber adjacent the air chamber, and a liquid-filled working chamber communicating with the hydraulic chamber. A working piston is provided in the working chamber and carries a chuck for grasping a mandrel of a blind rivet. This working piston is displaceable in the working chamber between a ready position wherein a mandrel can be fitted into the chuck and an actuated position wherein the chuck is retracted. An air piston is provided in the air chamber and subdivides it into a front compartment and a rear compartment. This air piston is displaceable between a front position and a rear position. The housing is formed with a front end of the front compartment with the first throughgoing hole for gas flow between the front compartment and the atmosphere. A hydraulic piston is carried on the air piston and is displaceable in the hydraulic chamber between an advanced position pressurizing the hydraulic chamber and corresponding to the front position of the air piston and a retracted position corresponding to the rear position of the air piston. A first valve is provided for admitting pressurized air into the rear compartment and thereby displacing the air piston into the front position, simultaneously displacing the hydraulic piston into the advanced position and displacing the working piston into the actuated position. A spring is braced between the housing and the working piston and urges this working piston into its ready position. Thus displacement of the working piston by the spring from the retracted position into the ready position automatically displaces the air piston into its rear position. The air in the rear compartment is usually driven out of the housing through the structure of the actuating valve which is intentionally made with loose tolerances so as to allow such leakage.
A disadvantage of such devices is, however, that the user must wait for the device to return to the ready condition after he has set a clinch nut. This is due to the fact that the pneumatic piston is pushed back into its starting position by the spring which is effective on the hydraulic piston that is connected to the mandrel-holding chuck. Thus once the trigger valve is released the return spring on the hydraulic piston attached to the chuck urges this element into its starting position thereby pressurizing the hydraulic chamber of the tool, and pressing back the pneumatic piston of the apparatus, which carries a piston that itself pressurizes the hydraulic chamber of the apparatus. Air in the pneumatic chamber must bleed out through the filling opening, and usually over the operator's hand so that a relatively long time elapses before the device is ready to use again. In addition the rush of air over the operator's hand has often found to be uncomfortable and to lead to the fouling of the device.
It has been suggested to overcome this difficulty by providing a larger inlet passage for the pneumatic chamber. This, however, requires greater pressure to operate the device and therefore slows down the operating time of the apparatus, although it does indeed decrease the time required for the tool to reset itself. The provision of a pressure-relief valve in the pneumatic chamber in no way decreases recycling time. A manually operated fast-acting bleed valve has been suggested, but this merely adds to the task of the operator.